1. Field of the Invention
This invention relates to multi-purpose radio systems, and more particularly to an interface (AVIU) between an aircraft communication, addressing and reporting system (ACARS) and VHF transceiver.
2. Problem Statement
The interface between the ARINC 724/724B Aircraft Communication, Addressing, and Reporting System (ACARS) management unit (MU) and the ARINC 716 VHF transceiver includes two discrete analog signals. The port select discrete is used by the ACARS to command the VHF radio to use the ACARS-provided tuning information (Transmitted from the ACARS using a digital ARINC 429 data bus). The selection of the ACARS tuning is made when the radio detects a path-to-ground on the port select discrete. The voice/data discrete is used by the ACARS to command the VHF radio to use the ACARS-provided audio signal when the ACARS-provided keyline is "closed." The selection of ACARS keying is made when the radio detects a path-to-ground on the voice/data discrete.
The use of ACARS discretes to control transmission and tuning in effect makes the VHF radio an extension of the ACARS, ACARS software is certificated to the DO-178A level 3, non-essential. ACARS is considered non-essential equipment. The VHF radio systems are certificated as essential equipment. The connection of ACARS in the manner described above degrades the VHF integrity to that of ACARS, in effect making the radio(s) connected to ACARS non-essential equipment. The FAA has rules that a radio with an interface to ACARS, as described above, may not be used for ATC communication.